The present invention relates generally to radar systems intended for a variety of applications including automotive and industrial applications.
A radar apparatus transmits a radar signal, which is reflected from multiple obstacles to create a received signal. The radar apparatus uses the received signal to estimate the distance, the velocity and the angle of arrival of these obstacles.
Continuous-Wave (CW) radars transmit either an unmodulated or modulated frequency carrier as the radar signal. A simple unmodulated signal can only detect the velocity and not range of a single object, and hence is not useful in applications where both range and relative velocity of multiple objects need to be simultaneously determined. In order to measure range, modulation of the radar signal is essential.
Frequency chirp architecture is the most popular of the automotive CW radars. In frequency-chirped radars, the frequency of the radar signal is varied according to a pre-determined pattern. The most widely used patterns are (a) frequency-stepped, in which frequency is changed by a step in each time period and (b) Linear Frequency Modulation (LFMCW), often referred to simply as FMCW, in which transmit frequency is changed continuously within each time period. This varying frequency essentially widens the bandwidth of the radar signal, which is equivalent to narrowing the signal in the time-domain. An FMCW radar can simultaneously estimate both the velocity and range of multiple objects.
For ease of explanation, some aspects of the prior art and the invention are discussed with respect to a radar apparatus which uses a frequency modulated continuous wave (FMCW) signal.
FIG. 1 shows diagram 100, which illustrates a conventional automotive object detection application.
As shown in the figure, diagram 100 includes a car 102, a radar transceiver 103, a radar beam 104, an object 106, an object 108, an object 110, a reflected wave 112, a reflected wave 114 and a reflected wave 116.
Object 106, object 108 and object 110 are arranged to be within the coverage range of radar beam 104 and are additionally arranged to have different distances from car 102, different bearings to car 102, and different velocities. Radar transceiver 103 is operable to transmit radar beam 104, to receive reflections from objects within the beam and to determine distance, velocity and arrival angle. Object 106 produces reflected wave 112, object 108 produces reflected wave 114 and object 110 produces reflected wave 116.
Radar beam 104 comprises a continuous series of transmitted frequency modulated “chirps”, each chirp being a short period of radar carrier transmission ramping in frequency from, for example, 77 GHz to 81 GHz. For any transmitted chirp, reflected wave 112, reflected wave 114 and reflected wave 116 each will arrive back at radar transceiver 103 at a different time, with a different Doppler and at a different arrival angle.
An object's distance, velocity, and angle within the beam can be ascertained by analyzing the properties of their reflected waves. For chirped radar, both the velocity and distance of an object from radar transceiver 103 can be ascertained by analyzing the spectrum of the received signals. Since transceiver 103 has a plurality of receive antennas in the form of an antenna array, the angle of arrival of the reflected waves can be ascertained by analyzing the reflected wave reception across the antennas comprising the array.
FIG. 2 shows a conventional FMCW type of radar system 200 with one transmit and one receive antenna.
As shown in the figure, system 200 includes ramp generating component 202, transmit antenna 204, a local oscillator 208, a receive antenna 212, a mixer 216, an analog to digital converter (ADC) 220 and a digital signal processor (DSP) 224.
Ramp generating component 202 is arranged to receive signals from local oscillator 208 on line 210 and to connect to transmit antenna 204, via line 206. Mixer 216 is arranged to receive signals from receive antenna 212 on line 214, to receive signals from ramp generating component 202 on line 206 and to send signals to ADC 220. DSP 224 receives signals from ADC 220 via line 222.
Local oscillator 208 is operable to provide reference signals (such as timing and/or reference frequencies) to ramp generating component 202. Ramp generating component 202 is operable to generate frequency ramp signals and transmit antenna 204 is operable to transmit those signals over the air. In some embodiments, the local oscillator itself may provide a frequency ramp centered around a lower frequency which may then be translated to the frequency of transmission by a ramp generator. Receive antenna 212 is operable to receive signals over the air. Mixer 216 is operable to apply a frequency mixing function. ADC 220 is operable to convert analog signals to digital signals and DSP 224 to process the digital signals.
A chirped CW signal is generated at ramp generating component 202 based on the input from local oscillator 208, and is transmitted over the air by transmit antenna 204. The transmitted chirped signal reflects from objects within the range and coverage of the radar beam and the reflected signals are received at antenna 212 and then are passed to mixer 216. Mixer 216 mixes the received signal with the transmitted frequency ramp to produce an analog intermediate frequency (IF) signal on line 218. The analog IF signal is sampled by ADC 220 to produce a digital IF signal on line 222. The digital IF signal is then processed and analyzed by DSP 224 to determine velocity and range of objects within the beam.
System 200 contains only one receive antenna, and as such, is not disposed to resolve the angle of arrival of reflected signals from objects and thus their locations. The resolution of angles of arrival is achieved through the use of a receive antenna array. The more antennas that comprise the array, i.e., the longer the array, the higher the resolution possible. Gesture recognition and some automotive applications, in particular, can require high resolution measurements of arrival angle.
FIG. 3 shows a prior art radar system 300 implementing a receive antenna array by using a plurality of identical integrated circuits or “chips” to support a plurality of receive antennas.
As shown in the figure, system 300 includes a radar chip 302, a radar chip 304, and a receiver antenna array 306. Receiver antenna array 306 includes a line 308, a line 310, a line 312, a line 314, a line 316 and a line 318.
Antenna array 306 is arranged to contain six antennas and is operable to receive reflected radar signals over the air. Line 308, line 310 and line 312, line 314, line 316 and line 318 are arranged to connect the antennas of antenna array 306 to radar chip 302 and radar chip 304.
Radar chip 302 and radar chip 304 are operable to provide both transmit and receive radar functions. Since this discussion involves only receive functions, transmit functions will not be covered for this figure. Radar chip 302 and radar chip 304 are further operable to provide functions for a plurality of external receive antennas. Each of radar chip 302 and radar chip 304 can support receive functions for up to three antennas.
Line 308, line 310 and line 312, line 314, line 316 and line 318 operate at RF frequencies in the region of 77 GHz. External lines and connectors design to support signals at such high frequencies are very specialized, very lossy and very costly, as is circuit board routing of such signals.
It is advantageous, therefore, in a radar apparatus to have the antennas integrated onto the package. This allows for a very integrated and cost effective solution. However, limitations on the number of channels on a single chip and the package size can limit the number of antennas that can be integrated in this way. In addition, the limited number of antennas can in turn limit the angle resolution achievable with such a radar apparatus. Techniques by which multiple radar chips with integrated antennas can be tiled together to improve the angle resolution are thus desirable.
FIG. 4 shows a prior art radar system 400 employing a plurality of radar chips with integrated antennas and chip tiling.
As shown in the figure, system 400 includes a radar chip 402, a radar chip 404 and an arrowed line 405. Radar chip 402 further includes transmit antenna 406, receive antenna 408 and receive antenna 410. Radar chip 404 further includes receive antenna 412 and receive antenna 414.
Radar chip 402 and radar chip 404 are arranged as a tiled pair and are as close as physically possible. Transmit antenna 406 is arranged as shown in the figure at the bottom of radar chip 402. Receive antenna 408 and receive antenna 410 are arranged as shown in the figure at the top of radar chip 402.
Additionally, the distance between receive antenna 408 and receive antenna 410 represents the distance required for antenna array formation at the frequency of operation. This is typically half the wavelength of operation. Receive antenna 412 and receive antenna 414 are arranged as shown in the figure at the top of radar chip 404. Again, the distance between receive antenna 412 and receive antenna 414 represents the distance required for antenna array formation at the frequency of operation. Arrowed line 405 is arranged between receive antenna 410 and receive antenna 412.
Radar chip 402 is operable to provide radar transmit and receive functions. Radar chip 404 is operable to provide radar receive functions. Radar chip 404 is also operable to provide transmit functions but these are unused. Receive antennas 408, 410, 412 and 414 are all operable to receive radar signals over the air.
System 400 is an attempt to tile two radar chips together to form a receive antenna array with four antennas. However, even though radar chip 402 and radar chip 404 are tiled together as closely as possible, the distance D as indicated by arrowed line 405 is much too large for the antennas to form a usable array across all four antennas, and this arrangement would not work. While in some cases it may be possible to change the dimensions of the chips or the position of the antennas on the chips, this would lead to constant customization of chips to specific applications.
It has already been explained that in attempting to employ multiple radar chips to form the long receive antenna arrays required for the high arrival angle resolutions needed by common applications, the use of external antennas is a difficult and very costly approach.
It has also been explained how solutions which use multiple radar chips with integrated antennas are severely limited by necessary restrictions on chip size, antenna spacing and chip spacing.
It should be noted that due to differing signal path lengths, component variability, differing temperatures, etc., between radar chips in a tiled configuration, calibration and synchronization techniques would have to be applied in order for the chips to work in conjunction with each other.
What is needed are systems and methods for implementing long receive antenna arrays employing the tiling of a plurality of standard radar chips that can overcome the geometric problems conventionally encountered, thus avoiding the extensive radar chip customization otherwise necessary and eliminating the many disadvantages of conventional, costly external antenna arrangements.